The reaction chemistry of cadmium telluride (CdTe) organometallic vapor-phase epitaxy (OMVPE) from dimethylcadmium (DMCd), dimethyltelluride (DMTe), and diisopropyltelluride (DIF'Te) has been studied by using on-line gas chromatography and numerical simulation. The organometallic compounds decompose on the CdTe surface by desorbing both alkyl radicals and hydrocarbon molecules. Gas-phase methyl radicals were detected by injecting ethylene, which reacted with the radicals and produced propane and other longer chain hydrocarbons. Methyl radicals from DMCd and hydrogen gas were found to be essential for DMTe decomposition. This suggests that H atoms, produced by the reaction of CH3-with Hz, adsorb onto the CdTe and hydrogenate the methyl groups bound to Te sites. The large amount of ethane, isobutane 2,3-dimethylbutane, and propylene produced from DMCd and DIPTe decomposition in hydrogen indicates that a substantial fraction of the alkyl groups recombine and disproportionate on the semiconductor surface. In summary, this study has revealed that the deposition of CdTe from organometallic compounds occurs by a free-radical mechanism, which involves adsorption of the compounds, desorption of alkyl radicals, and the simultaneous hydrogenation, recombination, and disproportionation of alkyl species on the surface and in the gas phase.

The reaction chemistry of zinc telluride (ZnTe) metalorganic vapor-phase epitaxy (MOVPE) from dimethylzinc (DMZn), diethylzinc (DEZn), and diisopropyltelluride (DIPTe) has been studied using on-line gas chromatography and infrared spectroscopy. Two growth regimes have been discovered: one at low values of the II/VI ratio and the other at higher values of the II/VI ratio. In the first regime, the group VI compound is consumed in excess, while in the second regime, the group II compound is consumed in excess. The crossover point lies at II/VI ) 5.0 for DMZn and at II/VI ) 0.3 for DEZn. Stoichiometric ZnTe is deposited under all growth conditions. The excess DIPTe consumed is converted into volatile diisopropylditelluride and isopropyltellurol. Conversely, the excess DEZn or DMZn consumed produces zinc metal. These waste byproducts accumulate in the outlet of the reactor. The hydrocarbon products generated from the ethyl and isopropyl ligands are indicative of radical disproportionation, recombination, and hydrogenation reactions. However, the methyl ligands mainly undergo surface hydrogenation to produce methane.

The metalorganic vapor-phase epitaxy (MOVPE) of cadmium zinc telluride (Cd1 - y Zn y Te) from dimethylcadmium (DMCd), dimethylzinc (DMZn), diethylzinc (DEZn), and diisopropyltelluride (DIPTe) was studied using on-line infrared spectroscopy to monitor the feed and effluent gases. The film composition was measured by X-ray diffraction. No zinc was incorporated into the film when DMCd and DMZn were used due to the very low reactivity of the latter compound. When DMCd and DEZn are tried, the films were nonuniform with Cd-rich films deposited at the reactor inlet and Zn-rich films deposited near the reactor outlet. This film profile was due to alkyl ligand exchange reactions between the group II precursors in the feed, producing DMZn, methylethylzinc (MEZn), methylethylcadmium (MECd), and diethylcadmium (DECd). The decomposition rates of these precursors vary over a wide range with DECd reacting at a 250 K lower temperature than DMZn. Since the organocadmium compounds were consumed at a much faster rate, CdTe was deposited first, while ZnTe was deposited downstream. The ligand exchange reactions explain why previous workers found it difficult to grow Cd1 - y Zn y Te alloys of uniform composition by MOVPE.